import java.util.*;
class Student{
	String id;
	String name;
	public Student(String id,String name){
		this.id = id;
		this.name = name;
	}
	public String toString(){
		return id + ":" +name; 
	}
}

public class Example10{
	public static void main(String[] args){
		HashSet hs = new HashSet();
		Student stu1 = new Student ("1","Jack");
		Student stu2 = new Student ("2","Rose");
		Student stu3 = new Student ("2","Rose");
		hs.add(stu1);
		hs.add(stu2);
		hs.add(stu3);
		System.out.println(hs);
	}
}